U.S. patent application No. 4,768,446 issued 6 Sept. 1988 to Wilkes et al and assigned to the assignee of this invention describes an external combustion system for a gas turbine engine. The combustion system has a pulverized coal fueled rich zone combustor, a quench stage, an inertial particle separator for removing heavy solids and ash from the combustion products of the rich zone combustor, a cyclone separator for removing finer solids and ash from the combustion products of the rich zone combustor, a lean zone combustor, and a dilution stage for cooling the combustion products of the lean zone combustor to a turbine inlet temperature compatible with current gas turbine engine technology. An external combustor according to this invention incorporates in a single unit the cyclone separator, the lean zone combustor, and the dilution stage to achieve manufacturing economy.